BACKGROUND: Although the mortality from bariatric surgery is low, perioperative determinants of morbidity and mortality in the bariatric surgery population to date have not been fully defined. This study aimed to evaluate the factors capable of predicting perioperative mortality based on preoperative characteristics with a national patient sample. METHODS: From the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database, all the primary bariatric procedures performed between 2007 and 2009 were identified. Using univariate analysis, factors associated with increased perioperative (30-day) mortality were identified. Logistic regression was used to select correlates of 30-day mortality, which were subsequently integrated into a simplified clinical scoring system based on the number of comorbid risk factors. RESULTS: The study identified 44,408 patients (79 % women, 21 % men) with a mean age of 45 ± 11 years. The cumulative 30-day perioperative mortality rate was 0.14 %. The majority of the procedures performed included laparoscopic gastric bypass (54 %) followed by laparoscopic gastric banding (33 %) and open gastric bypass (7 %). Independent predictors associated with significantly increased mortality included age >45 years [adjusted odds ratio (AOR), 2.45], male gender (AOR = 1.77), a body mass index (BMI) of 50 kg/m(2) or higher (AOR, 2.48), open bariatric procedures (AOR, 2.34), diabetes (AOR, 2.88), functional status of total dependency before surgery (AOR, 27.6), prior coronary intervention (AOR, 2.66), dyspnea at preoperative evaluation (AOR, 4.64), more than 10 % unintentional weight loss in 6 months (AOR, 13.5), and bleeding disorder (AOR, 2.63). Ethnicity, hypertension, alcohol abuse, liver disease, and smoking had no significant association with mortality in this study. Risk stratification based on the number of preoperative comorbid factors showed an exponential increase in mortality as follows: 0-1 comorbidities (0.03 %), 2-3 comorbidities (0.16 %), and 4 comorbidities or more (7.4 %). CONCLUSION: This model provides a straightforward, precise, and easily applicable tool for identifying bariatric patients at low, intermediate, and high risk for in-hospital mortality. Notably, baseline functional status before surgery is the single most powerful predictor of perioperative survival and should be incorporated into risk stratification models.